1. Field of the Invention
The present invention relates to a nitride semiconductor device and a manufacturing method thereof, and more particularly, to a nitride semiconductor device with p/n-type nitride layer gate electrodes, and a manufacturing method thereof.
2. Description of the Related Art
There has been growing interest in reduction of power consumption due to green energy policy. To achieve this, improvement in power conversion efficiency is an essential element. In the power conversion, efficiency of a power switching device has influence on the entire power conversion efficiency.
At present, most of power devices generally used are power MOSFETs or IGBTs using silicon. However, an increase in efficiency of the devices is limited due to material limitations of silicon. To overcome this, there have been patent applications which are to increase the conversion efficiency by manufacturing a transistor using a nitride semiconductor such as gallium nitride (GaN).
However, a transistor having an HEMT structure using GaN becomes ‘on’ state in which current flows due to low resistance between drain and source when a gate voltage is 0V (normal state) and thus causes current and power consumption. In this normally-on structure, there is a disadvantage that a negative voltage (for example, −5V) should be applied to gate to convert the normally-on state into off state.
To overcome this advantage, a technique of making a normally-off structure by employing a gate electrode structure using p-type GaN on an AlGaN/GaN HEMT structure has been developed. For example, in U.S. patent U.S. Pat. No. 7,816,707, a high current device through enhanced mode and hole injection is implemented by applying p-GaN or p-AlGaN gate onto an AlGaN/GaN structure. Further, in U.S. patent U.S. Pat. No. 7,728,356, an enhanced mode GaN HEMT is implemented by applying p-GaN gate onto an AlGaN/AlN/GaN structure. That is, in U.S. Pat. No. 7,816,707 and U.S. Pat. No. 7,728,356, a GaN HFET implements normally-off by forming p-type GaN or p-type AlGaN in a gate electrode to deplete 2DEG below the gate.